This invention relates to a digital portable telephone unit suited to play back excellent voice/sound and a method for playing back voice/sound in the digital portable telephone unit.
In order to play back excellent voice/sound in digital portable telephone units, it is necessary to measure precisely RSSI (receive signal strength indicator) to each symbol point.
FIG. 1 shows an example of conventional digital portable telephone unit trying such a RSSI measurement.
As shown in FIG.1, receive signal received by an antenna 101 is selected at a desired receive frequency, frequency-converted and amplified by a radio section 102. Then, IF (intermediate frequency) 127 and RSSI (receive signal strength indicator) are output from the radio section 102 to a demodulation section 103.
IF 127 output to the demodulation section 103 is demodulated and then output, as receive data, to an A/D converter 114. The A/D converter 114 digitalizes RSSI voltage of RSSI 127a and then outputs it.
Concurrently, a control section 109 processes the receive data and outputs voice/sound signal. Also, the control section 109 uses the digitalized RSSI 127a for the control of phone-call connection. Voice/sound signal processed by the control section 109 is then converted into analogue signal by an audio processing section 106, and then is output from a receiver 113.
On the other hand, voice/sound input from a microphone 112 is converted into digital signal by the audio processing section 106. The control section 109 conducts the processing to process the voice/sound digital signal into transmit data. After that processing, the transmit data signal is modulated by the radio section 102, into carrier wave with a normal frequency. Then, the carrier-wave signal with the normal frequency is amplified by the radio section 102, and then is transmitted through the antenna 101.
Meanwhile, an operation section 110 controls the user interface to send contents of instruction such as a phone number etc. from the user to the control section 109. Also, a display section 111 displays various information such as a received phone number etc. A CLK section 105 generates a clock for timing processing, time display etc. A reference oscillator 108 generates a reference frequency used in generating frequency at the radio section 102 and a precise frequency used in the control section 109 and the demodulation section 103.
An AFC (automatic frequency control) section 104 controls the reference oscillator 108 to coincide with a precise received frequency of base station.
FIG.2 shows the detailed composition of the demodulation section 103.
In digital portable telephone units, xcfx80/4 shift DQPSK is used as modulation system. In modulation, delay detection system is used.
Thus, IF 127 from the radio section 102 is output as phase DATA 129 at a timing of symbol CLK 132 by a phase detection section 121 which operates using a reference frequency of 14.4 MHz 128 as a clock.
A DATA playback section 122 produces demodulated data 133 from the phase DATA 129 and outputs it. Also, a phase correction section 123 makes a phase correction based on the phase DATA 129, and outputs a phase-corrected IF 127 to be used at the AFC section 104 as corrected output 130.
A demodulation CLK section 125 outputs a demodulation CLK of 2.68 MHz 134 to a CLK regenerative section 124. Here, between the demodulation CLK section 125 and the CLK regenerative-section 124 is composed as a PLL (phase-locked loop) circuit.
The CLK regenerative section 124 outputs symbol CLK 132 (21 kHz) obtained dividing 2.68 MHz demodulation CLK 134 by 128 and DATA CLK (42 kHz) 131 obtained dividing it by 64.
Also, the phase timings of symbol CLK 132 and DATA CLK 131 are adjusted according to the difference in the amount of phase shift between first-half and second-half symbol sections of phase DATA 129, so that they are made to coincide with the symbol timing of IF signal 127.
Meanwhile, as a system to decode encoded audio data more excellently, a method of incorporating RSSI as a factor of decoding operation is known.
In this case, it is necessary to measure precisely RSSI to each symbol point of receive signal digital-modulated.
Here, the xcfx80/4 shift DQPSK is characterized in that the signal level at each symbol point becomes constant, however, between symbol points, the signal level varies depending on data values modulated.
So, in order to measure precisely RSSI to each symbol point, it is important to measure the signal level at a precise timing of symbol point.
Accordingly, it is an object of the invention to provide a digital portable telephone unit that offers an excellent playback of voice/sound by measuring signal level precisely at a timing of symbol point.
It is a further object of the invention to provide a method for playing back voice/sound that offers an excellent-playback of voice/sound by measuring signal level precisely at a timing of symbol point.
According to the invention, a digital portable telephone unit, comprises:
an antenna through which signal is transmitted and received;
a radio section which conducts the frequency conversion of signal and outputs IF (intermediate frequency) and RSSI (receive signal strength indicator);
a demodulation section which demodulates the IF to output receive data;
an A/D converter which outputs digitalizing the voltage of RSSI; and
a control section which receives the receive data and outputs audio signal;
wherein the demodulation section outputs a trigger to indicate a symbol point of RSSI to the A/D converter.
According to another aspect of the invention, a method for playing back voice/sound, comprises:
first step of conducting the transmission/reception of signal;
second step of conducting the frequency conversion of signal and outputting IF (intermediate frequency) and RSSI (receive signal strength indicator);
third step of demodulating the IF to output receive data;
fourth step of outputting digitalizing the voltage of RSSI;
fifth step of processing the receive data to output audio signal; and
sixth step of outputting a trigger to indicate a symbol point when digitalizing the voltage of RSSI.